1. Field of the Invention
The present invention relates to a method of manufacturing a wiring and a conductive layer. More specifically, the present invention relates to a method of manufacturing a wiring and a conductive layer over an insulating surface, a semiconductor device, and a display device by droplet discharging method.
2. Description of the Related Art
A thin film transistor (hereinafter referred to as a TFT) formed by using a thin film on an insulating surface is widely applied to integrated circuits and the like. Application of a display panel using TFTs greatly expands, in particular, into a large-scale display device. Thus higher definition, higher aperture ratio, superior reliability and growth in size for a screen have been extremely required.
According to the foregoing requirements, research has been actively carried out. Therefore, in order to enhance competitiveness of products, the fabrication of products, which is superior in cost effectiveness, is an indispensable condition in addition to fulfilling the above-mentioned requirements.
As a method for manufacturing the wiring in the thin film transistor, a method in which the entire surface of a substrate is coated with a conductive layer and an etching treatment is subsequently performed by using a mask can be noted (refer to Patent Document 1).
[Patent Document 1] Japanese Patent Laid Open No. 2002-359246
A sophisticated display device has also been increasingly required, and therefore an attempt to simultaneously form a display panel along with a driving circuit, a central processing unit (CPU), and the like on a same substrate has been carried out.
Further, in the case of forming a wiring according to the above-mentioned Patent Document 1, for example, when an ICP etching apparatus is used, in accordance with etching conditions such as bias power density, ICP power density, pressure, total flow of etching gases, an additive ratio of oxygen and a temperature of a lower electrode are increased, selective ratio of a resist and a conductive layer vary and the length or width of the conductive layer varies on the substrate.
In addition, in the case of performing an etching treatment, since an additional process for manufacturing a mask made of photoresist etc. is required, the number of processes is increased. Furthermore, wasted materials are generated since the etching treatment is performed so as to make the conductive film into a predetermined shape after the conductive layer is formed over the entire surface. In particular, a resist material used in patterning is extremely expensive, which adversely affects the costs of end products.
Further, materials used for etched portions or materials used for unused portions are removed, and eventually become waste fluids to dispose. In recent years, since awareness concerning environment has been raised, it is indispensable that the waste fluids are adequately treated and disposed. However, a huge amount of capital investment and costs are required for the disposal of the waste fluids. This problem is a significant obstacle to price reduction of manufactured goods. As a matter of course, such wasted materials are only disposed, which results in a waste of resources.
These problems become more serious when a wiring is formed over the large size substrate of which side exceeds 1.0 m.
On the other hand, a method of carrying out the patterning directly on the substrate by droplet discharging method has been beginning to be considered in recent years. Concerning this method, for example, a method of forming a wiring or electrode pattern directly on the substrate by using a special kind of ink in which metal microparticles are dispersed into a liquid solution has been proposed. Further, another method of forming such pattern by directly discharging resist by droplet discharging method is also proposed instead of carrying out the patterning by using a mask in the same manner as conventional photolithography.
However, when wirings are formed by droplet discharging method, there is a possibility that contact holes are not completely filled, or step differences are generated on the surface of the wirings. In the case where the contact holes are not completely filled, the wirings over the portions are not sufficiently contacted, and therefore the wirings are likely to be disconnected. There is also a possibility that the resistivity is increased, or gas (such as air) taken in the wirings is expanded in heating in the latter step, thereby causing disadvantages even if the wirings are completely connected. With respect to step differences generated over the surface of the wiring, when layers are laminated on the step differences and depressions or projections are overlapped each other, the step differences are grown up, which ultimately results in disadvantages such as disconnection of the wirings. These problems are serious in reliability.
Furthermore, the phenomena in which a liquid droplet containing conductive compositions is jetted and adhered to a substrate to form a thin film pattern is an extremely complicated process. Further, characteristics of the thin film pattern are significantly affected by a drying step. That is, the characteristics vary according to the shape of the liquid droplet after the step of drying the liquid droplet, and therefore depend on the drying step of the liquid droplet. The drying step is very difficult to be controlled, and hence, the control of the drying step becomes one of major problems for providing stable products.